Visualization of anatomical cavities

ABSTRACT

Described embodiments include a system that includes a display and a processor. The processor is configured to modify an image slice by filling a portion, of the image slice, that corresponds to an anatomical cavity with a representation of a wall of the anatomical cavity, and to display the modified image slice on the display. Other embodiments are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to an application entitled“Visualization of distances to walls of anatomical cavities,” attorneyref. no. 1002-1461/ID-840/BIO5679USNP, filed on even date herewith,whose disclosure is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of medical images.

BACKGROUND

A computerized tomography (CT) scan acquires the radiodensity, alsotermed radiopacity, of the scanned portion of anatomy. Radiodensity ismeasured in Hounsfield units (HU), with air having HU=−1000, waterhaving HU=0, and cortical bone having HU=+3000. In a CT image, theacquired radiodensity values are mapped to different grayscale values.Typically, in a CT image, air is presented in black, cortical bone inwhite, and other materials in varying shades of gray.

Traditionally, interventional radiologists have been trained to navigatethe head of a subject using two-dimensional (2D) images of the head. Forexample, during a sinus procedure, the interventional radiologist mayrefer to three computerized tomography (CT) slices of the subject'shead: an axial slice, a coronal slice, and a sagittal slice.

U.S. Pat. No. 8,532,738, whose disclosure is incorporated herein byreference, describes a method, including constructing a simulatedsurface of a body cavity, and pressing a distal end of a probe against awall of the body cavity. While pressing the distal end against the wall,position measurements are accepted from the probe indicating a positionof the probe within the body cavity, and force measurements are acceptedfrom the probe indicating a force between the distal end and the wall. Adistortion in the simulated surface is created at the position indicatedby the position measurements, so as to form a distorted surface, upondetecting that the force measurements exceed a predefined amount. Thedistorted surface is then displayed.

U.S. Pat. No. 7,924,279, whose disclosure is incorporated herein byreference, describes a system for visualizing a 3D volume, in particularfor medical applications, that includes an input for receiving athree-dimensional set of data representing voxel values of the 3Dvolume. The data set is stored in a storage. A processor projects thevolume onto an imaginary 2D projection screen from a predeterminedviewpoint. For each pixel of the 2D projection image a ray is castthrough the pixel and through the volume. A protocol is used that, whiletraversing along ray positions within the volume, determines a renderingalgorithm and/or rendering parameters in dependence on the ray position.For each ray position the determined rendering algorithm/parameters areused to calculate a contribution to a pixel value of the pixel based onat least one voxel value within a predetermined range of the rayposition. An output is used for providing pixel values of a 2D image forrendering on a display.

SUMMARY OF THE INVENTION

There is provided, in accordance with some embodiments of the presentinvention, a system that includes a display and a processor. Theprocessor is configured to modify an image slice by filling a portion,of the image slice, that corresponds to an anatomical cavity with arepresentation of a wall of the anatomical cavity, and to display themodified image slice on the display.

In some embodiments, the processor is further configured to identify theportion of the image slice that corresponds to the anatomical cavity.

In some embodiments, the processor is configured to modify the portionof the image slice that corresponds to the anatomical cavity withoutmodifying other portions of the image slice.

In some embodiments, the processor is further configured to compute therepresentation by rendering the wall of the cavity.

In some embodiments, the processor is configured to render the wall ofthe cavity in color.

In some embodiments, the wall of the cavity is located behind a locationat which the image slice was acquired.

In some embodiments, the image slice is a computed tomography (CT) imageslice.

In some embodiments, the processor is further configured to overlay anicon that represents an intrabody tool on a portion of the modifiedimage slice that corresponds to a location of the intrabody tool withinthe anatomical cavity.

In some embodiments, the processor is further configured to overlay amarker on a portion of the representation of the wall that correspondsto a location at which the intrabody tool would meet the wall, were theintrabody tool to continue moving toward the wall in a direction inwhich the intrabody tool is pointing.

In some embodiments, the processor is further configured to identify thelocation at which the intrabody tool would meet the wall, by projectinga virtual ray from a distal tip of the intrabody tool.

There is further provided, in accordance with some embodiments of thepresent invention, a method that includes, using a processor, modifyingan image slice by filling a portion, of the image slice, thatcorresponds to an anatomical cavity with a representation of a wall ofthe anatomical cavity, and displaying the modified image slice.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system for guiding a medicalprocedure, in accordance with some embodiments of the present invention;and

FIG. 2 shows an original CT image slice and a modified CT image slice,in accordance with some embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

As noted above, interventional radiologists typically use 2D images (or“slices”) for navigation. A challenge in using 2D images, however, isthe lack of depth information contained in such images. For example,when using 2D images to navigate a catheter within an anatomical cavity,it may be difficult to ascertain the distance between the catheter andthe wall of the cavity.

Embodiments of the present invention address this challenge, byproviding an enhanced presentation of anatomical cavities in 2D images.In this enhanced presentation, the cavity is given a three-dimensional(3D) appearance, via the incorporation of morphological information frombeneath the displayed 2D slice. For example, a processor may“illuminate” the cavity with a virtual light source, such that the wallsof the cavity, beneath the displayed 2D slice, are “visible” to avirtual camera positioned near the virtual light source. The cavitywalls may then be rendered, in color, with varying shades of brightness,corresponding to the view of the virtual camera.

Some embodiments enhance the image further, by overlaying, on the image,an icon that represents the catheter, along with a marker that indicatesthe distance of the catheter from the cavity wall. To produce themarker, a processor may project a virtual ray from the tip of thecatheter, and show the marker, in the image, at the point at which thevirtual ray hits the cavity wall.

System Description

Reference is initially made to FIG. 1, which is a schematic illustrationof a system 20 for guiding a medical procedure, in accordance with someembodiments of the present invention.

FIG. 1 depicts a physician 26 performing a procedure on a subject 22.During this procedure, physician 26 inserts an intrabody tool 28, suchas a catheter, into a nasal cavity and/or a sinus of subject 22, andthen uses tool 28 to probe, and/or operate on, the nasal cavity and/orsinus. Typically, the location and orientation of the tool is tracked,using, for example, a magnetic tracking system. For example, system 20may comprise one or more magnetic-field generators 24, which, during theprocedure, generate respective magnetic fields. These fields inducerespective voltages in one or more magnetic sensors coupled to tool 28.Based on these induced voltages, a processor 34 ascertains the locationand orientation of the tool with respect to the coordinate system of thetracking system.

Typically, prior to the procedure, a volume of the subject's head isacquired, using, for example, a CT scanner. Subsequently, during theprocedure, processor 34 displays, on a display 30, at least one imageslice 32, taken from the volume and enhanced as described below. Thephysician may then refer to slice 32, in deciding how to best navigatethe subject's nasal cavity and/or sinus.

It is noted that the term “image slice,” as used in the presentapplication (including the claims), refers to any two-dimensional imageacquired by imaging a particular cross-section of a three-dimensionalobject, or by taking a particular cross-section of a three-dimensionalimage of the object. (An image slice may be alternatively referred toherein simply as an “image” or a “slice.”) For example, prior to theprocedure, a volume of the subject's head may be acquired, by acquiringa stack of sagittal image slices at successive depths. Subsequently,processor 34 may derive an “image slice” from this volume, by taking anyone of the original sagittal image slices from the volume, or by takinga cross-section of the volume such as to derive a new slice havinganother suitable orientation. (Typically, the derivation of new slicesis performed prior to the procedure.)

Typically, prior to the procedure, processor 34 registers the magnetictracking system with the CT scanner, e.g., as described in U.S. patentapplication. Ser. No. 15/290,968, whose disclosure is incorporatedherein by reference. The output of this registration procedure is atransformation, which the processor subsequently uses to compute thelocation of the distal end of the intrabody tool with respect to imageslice 32.

In general, processor may be embodied as a single processor, or as acooperatively networked or clustered set of processors. Processor 34 istypically a programmed digital computing device comprising a centralprocessing unit (CPU), random access memory (RAM), non-volatilesecondary storage, such as a hard drive or CD ROM drive, networkinterfaces, and/or peripheral devices. Program code, including softwareprograms, and/or data are loaded into the RAM for execution andprocessing by the CPU and results are generated for display, output,transmittal, or storage, as is known in the art. The program code and/ordata may be downloaded to the computer in electronic form, over anetwork, for example, or it may, alternatively or additionally, beprovided and/or stored on non-transitory tangible media, such asmagnetic, optical, or electronic memory. Such program code and/or data,when provided to the processor, produce a machine or special-purposecomputer, configured to perform the tasks described herein.

Reference is now made to FIG. 2, which shows an original CT image slice31 and a modified CT image slice 32, in accordance with some embodimentsof the present invention.

As described above, a CT image typically presents air in black, corticalbone in white, and other materials in varying shades of gray. Forexample, image slice 31 includes a black portion, referred to herein asa void 36, corresponding to an anatomical cavity; in particular, void 36corresponds to a nasal cavity of the subject. (In other words, imageslice 31 “slices through” the nasal cavity, such that the interior ofthe nasal cavity appears in the image slice as void 36.) Image slice 31further includes a white or gray region 38, corresponding to bone and/orother tissue surrounding the nasal cavity.

In embodiments of the present invention, processor 34 modifies imageslice 31, such as to generate modified image slice 32. To modify imageslice 31, the processor first identifies portions of image slice 31 thatcorrespond to anatomical cavities, i.e., that were formed by theintersection of the scan plane of the scanner with the anatomicalcavities. (As described above, in CT images, these portions appear asvoids, such as void 36.) The processor then fills each of the identifiedportions with a representation of a wall of the corresponding anatomicalcavity, thus giving each anatomical cavity a three-dimensionalappearance. (Stated differently, the processor overlays, on eachidentified portion of the image, a three-dimensional (3D) view of thecorresponding anatomical cavity.) For example, in modified image slice32, void 36 is replaced with a three-dimensional representation 44 ofthe wall of the nasal cavity that is behind the location at which theimage slice was acquired (i.e., the wall is behind the scan plane,relative to the perspective of one who views the image).

The processor then displays modified image slice 32, as described abovewith reference to FIG. 1.

More generally, the processor may perform the modification describedherein for each image slice that shows part of an anatomical cavity.Typically, prior to the procedure, the processor iterates over all ofthe relevant image slices (both original and derived), and modifies eachcavity-containing image slice as described herein. Subsequently, duringthe procedure, the processor continually monitors the location of thetool, and, if the location of the tool has changed, the processor mayretrieve and display one or more modified image slices that pass throughthe new location of the tool. (It is noted that the processor mayalternatively modify an image slice, as described herein, in real-time,immediately prior to displaying the image slice.)

Typically, the processor computes representation 44, by rendering thewall of the cavity. First, the processor ascertains the form of the wallfrom the three-dimensional image from which image slice 31 was derived.The processor then uses any suitable rendering technique to render thewall. For example, the processor may illuminate the wall with a virtuallight source, and render the wall in accordance with the view of avirtual camera positioned near the virtual light source. The processorthen replaces the void in image slice 31 with the rendering. Typically,the wall is rendered in color, to help the physician differentiatebetween the anatomical cavity and the surrounding tissue.

Typically, the processor does not modify other portions of image slice31, such as region 38 of the image slice. For example, the processor maynot modify any portion of the image slice, other than the portioncorresponding to the anatomical cavity. Modified image slice 32 is thus,typically, a “hybrid” image, in that region 38 is shown as atwo-dimensional surface, in grayscale, while the wall of the anatomicalcavity is rendered as a three-dimensional surface, typically in color.

Reference is now specifically made to the schematic illustration at thebottom of FIG. 2, which reproduces a portion of modified image slice 32.

Typically, the processor further overlays, on modified image slice 32,an icon 40 that represents intrabody tool 28 (in particular, the distalend thereof) on a portion of modified image slice 32 that corresponds tothe location of the intrabody tool within the anatomical cavity.Typically, the processor also overlays a marker 42 on a portion ofrepresentation 44 that corresponds to a location at which the intrabodytool would meet the wall, were the intrabody tool to continue movingtoward the wall in the direction in which the intrabody tool ispointing. For example, the processor may project a virtual ray 46 fromthe distal tip of the intrabody tool, identify the location at whichvirtual ray 46 meets the wall of the anatomical cavity, and then overlaymarker 42 on the portion of representation 44 that corresponds to thislocation. (Although, for the sake of illustration, virtual ray 46 isshown in the schematic portion of FIG. 2, it is noted that virtual ray46 is typically not shown in modified image slice 32.) Icon 40, andmarker 42, generally facilitate navigation of the tool within theanatomical cavity, in that, for example, the distance between icon 40and marker 42 indicates the distance of the tool from the wall of thecavity.

In some embodiments, a fully three-dimensional image (i.e., an imagethat is fully rendered in three dimensions) displayed, instead ofmodified image slice 32 (which, as described above, is only partlyrendered in three dimensions), and icon 40 and/or marker 42 are overlaidon the representation of the anatomical wall in this image.

Although the description herein mainly relates to CT images, it is notedthat embodiments of the present invention may also be applied to imagesacquired using other modalities, such as magnetic resonance imaging(MRI). (In MRI images, anatomical cavities do not necessarily appear asvoids, but are nonetheless generally identifiable, such that they may beidentified and modified as described herein.)

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of embodiments of the presentinvention includes both combinations and subcombinations of the variousfeatures described hereinabove, as well as variations and modificationsthereof that are not in the prior art, which would occur to personsskilled in the art upon reading the foregoing description. Documentsincorporated by reference in the present patent application are to beconsidered an integral part of the application except that to the extentany terms are defined in these incorporated documents in a manner thatconflicts with the definitions made explicitly or implicitly in thepresent specification, only the definitions in the present specificationshould be considered.

The invention claimed is:
 1. A system for performing a procedure in anasal cavity and/or sinus, comprising: (a) a magnetic tracking system;(b) an intrabody tool having one or more magnetic sensors; (c) adisplay; (d) a memory configured to store an image slice and athree-dimensional model of a patient anatomy, wherein the image slice isa two-dimensional image, and wherein a plane location from which thepatient anatomy is shown in the image slice is present within thethree-dimensional model; (e) a processor, configured: (i) to identify aportion of the image slice that corresponds to an anatomical cavity,(ii) to identify a wall of the three-dimensional model that correspondsto the anatomical cavity, from the same plane location as that of theimage slice, (iii) to create a modified image slice by overlaying thewall on the anatomical cavity of the image slice, (iv) to overlay anicon that represents the intrabody tool on a portion of the modifiedimage slice that corresponds to a location of the intrabody tool withinthe anatomical cavity, and (v) to display the modified image slice onthe display.
 2. The system according to claim 1, wherein the modifiedimage slice is identical to the image slice, except for the area thatcorresponds to the anatomical cavity.
 3. The system according to claim1, wherein the processor is further configured to render the wall inthree dimensions.
 4. The system according to claim 3, wherein theprocessor is configured to render the wall in color, with varying shadesof brightness, to provide an indication of depth.
 5. The systemaccording to claim 1, wherein the image slice is a computed tomography(CT) image slice.
 6. The system according to claim 1, wherein theprocessor is further configured to overlay a marker on a portion of thewall that corresponds to a location at which the intrabody tool wouldmeet the wall, were the intrabody tool to continue moving toward thewall in a direction in which the intrabody tool is pointing.
 7. Thesystem according to claim 6, wherein the processor is further configuredto: (i) identify the location at which the intrabody tool would meet thewall, by projecting a virtual ray from a distal tip of the intrabodytool, and (ii) overlay a graphical representation of the virtual ray onthe modified image that begins at the icon and terminates at the marker.8. The system of claim 1, wherein the processor is further configuredto: (i) direct a virtual light source at a portion of the modified imagethat corresponds to the wall, (ii) direct a virtual camera at theportion of the modified image, and (iii) render the portion inaccordance with the view of the virtual camera.
 9. The system of claim8, wherein the processor is further configured to, when rendering theportion in accordance with the view of the virtual camera, render theportion in varying shades of brightness.
 10. The system of claim 9,wherein the processor is further configured to render the portion incolor and render other portions of the modified image in grayscale. 11.The system of claim 8, wherein the virtual camera is positionedproximate to the virtual light source.
 12. The system of claim 1,wherein the processor is configured to display a subsequent modifiedimage in response to a change in the location of the intrabody tool. 13.The system of claim 12, wherein the processor is configured to createthe modified image and the subsequent modified image in real-time,during a procedure, in response to changes in the location of theintrabody tool.
 14. A method for performing a procedure in a nasalcavity and/or sinus using a magnetic tracking system and an intrabodytool having one or more magnetic sensors, the method comprising: (a)using a processor, identifying a portion of the image slice thatcorresponds to an anatomical cavity; (b) storing, on a memory, an imageslice and a three-dimensional model of a patient anatomy, wherein theimage slice is a two-dimensional image, and wherein a plane locationfrom which the patient anatomy is shown in the image slice is presentwithin the three-dimensional model; (c) identifying a wall of thethree-dimensional model that corresponds to the anatomical cavity, fromthe same plane location as that of the image slice; (d) creating amodified image slice by overlaying the wall on the anatomical cavity ofthe image slice; (e) overlaying an icon that represents the intrabodytool on a portion of the modified image slice that corresponds to alocation of the intrabody tool within the anatomical cavity; and (f)displaying the modified image slice.
 15. The method according to claim14, further comprising rendering the wall in three dimensions.
 16. Themethod according to claim 15, wherein rendering the wall in threedimensions comprises rendering the wall of the cavity in color, withvarying shades of brightness, to provide an indication of depth.
 17. Themethod according to claim 14, wherein the image slice is a computedtomography (CT) image slice.
 18. The method according to claim 14,further comprising overlaying a marker on a portion of the wall thatcorresponds to a location at which the intrabody tool would meet thewall, were the intrabody tool to continue moving toward the wall in adirection in which the intrabody tool is pointing.
 19. The methodaccording to claim 18, further comprising: (a) identifying the locationat which the intrabody tool would meet the wall, by projecting a virtualray from a distal tip of the intrabody tool; and (b) overlaying agraphical representation of the virtual ray on the modified image thatbegins at the icon and terminates at the marker.
 20. A method forperforming a procedure in a nasal cavity using an intrabody tool havingone or more position sensors, the method comprising: (a) storing, on amemory, an image slice and a three-dimensional model of a patientanatomy, wherein the image slice is a two-dimensional image, and whereina plane location from which the patient anatomy is shown in the imageslice is present within the three-dimensional model; (b) using aprocessor, modifying the image slice by filling a portion of the imageslice that corresponds to the nasal cavity with a three-dimensionalrepresentation of a wall of the nasal cavity from the three dimensionalmodel, wherein the wall of the nasal cavity is located behind a planelocation at which the image slice was acquired; (c) identifying theportion of the image slice that corresponds to a real-time location ofthe intrabody tool the nasal cavity, wherein the real-time location ofthe intrabody tool in the nasal cavity is determined based on the one ormore position sensors of the intrabody tool; (d) overlaying an indicatoron a portion of the modified image slice, wherein the indicatorcorresponds to a real-time location of the intrabody tool within thenasal cavity; and (e) displaying the modified image slice, wherein themodified image slice comprises: (i) a two-dimensional representation ofthe plane location, (ii) the three-dimensional representation of thewall of the nasal cavity, and (iii) the indicator indicating thereal-time location of the intrabody tool within the nasal cavity.